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Python objects implemented in C can export a group of functions called the
“buffer interface.” These functions can be used by an object to expose its
data in a raw, byte-oriented format. Clients of the object can use the buffer
interface to access the object data directly, without needing to copy it
first.

Two examples of objects that support the buffer interface are strings and
arrays. The string object exposes the character contents in the buffer
interface’s byte-oriented form. An array can only expose its contents via the
old-style buffer interface. This limitation does not apply to Python 3,
where memoryview objects can be constructed from arrays, too.
Array elements may be multi-byte values.

An example user of the buffer interface is the file object’s write()
method. Any object that can export a series of bytes through the buffer
interface can be written to a file. There are a number of format codes to
PyArg_ParseTuple() that operate against an object’s buffer interface,
returning data from the target object.

Starting from version 1.6, Python has been providing Python-level buffer
objects and a C-level buffer API so that any built-in or used-defined type can
expose its characteristics. Both, however, have been deprecated because of
various shortcomings, and have been officially removed in Python 3 in favour
of a new C-level buffer API and a new Python-level object named
memoryview.

The new buffer API has been backported to Python 2.6, and the
memoryview object has been backported to Python 2.7. It is strongly
advised to use them rather than the old APIs, unless you are blocked from
doing so for compatibility reasons.

An array of Py_ssize_ts the length of ndim. If these
suboffset numbers are greater than or equal to 0, then the value stored
along the indicated dimension is a pointer and the suboffset value
dictates how many bytes to add to the pointer after de-referencing. A
suboffset value that it negative indicates that no de-referencing should
occur (striding in a contiguous memory block).

If all suboffsets are negative (i.e. no de-referencing is needed, then
this field must be NULL (the default value).

Here is a function that returns a pointer to the element in an N-D array
pointed to by an N-dimensional index when there are both non-NULL strides
and suboffsets:

This is a storage for the itemsize (in bytes) of each element of the
shared memory. It is technically un-necessary as it can be obtained
using PyBuffer_SizeFromFormat(), however an exporter may know
this information without parsing the format string and it is necessary
to know the itemsize for proper interpretation of striding. Therefore,
storing it is more convenient and faster.

This is for use internally by the exporting object. For example, this
might be re-cast as an integer by the exporter and used to store flags
about whether or not the shape, strides, and suboffsets arrays must be
freed when the buffer is released. The consumer should never alter this
value.

Export obj into a Py_buffer, view. These arguments must
never be NULL. The flags argument is a bit field indicating what
kind of buffer the caller is prepared to deal with and therefore what
kind of buffer the exporter is allowed to return. The buffer interface
allows for complicated memory sharing possibilities, but some caller may
not be able to handle all the complexity but may want to see if the
exporter will let them take a simpler view to its memory.

Some exporters may not be able to share memory in every possible way and
may need to raise errors to signal to some consumers that something is
just not possible. These errors should be a BufferError unless
there is another error that is actually causing the problem. The
exporter can use flags information to simplify how much of the
Py_buffer structure is filled in with non-default values and/or
raise an error if the object can’t support a simpler view of its memory.

0 is returned on success and -1 on error.

The following table gives possible values to the flags arguments.

Flag

Description

PyBUF_SIMPLE

This is the default flag state. The returned
buffer may or may not have writable memory. The
format of the data will be assumed to be unsigned
bytes. This is a “stand-alone” flag constant. It
never needs to be ‘|’d to the others. The exporter
will raise an error if it cannot provide such a
contiguous buffer of bytes.

PyBUF_WRITABLE

The returned buffer must be writable. If it is
not writable, then raise an error.

PyBUF_STRIDES

This implies PyBUF_ND. The returned
buffer must provide strides information (i.e. the
strides cannot be NULL). This would be used when
the consumer can handle strided, discontiguous
arrays. Handling strides automatically assumes
you can handle shape. The exporter can raise an
error if a strided representation of the data is
not possible (i.e. without the suboffsets).

PyBUF_ND

The returned buffer must provide shape
information. The memory will be assumed C-style
contiguous (last dimension varies the
fastest). The exporter may raise an error if it
cannot provide this kind of contiguous buffer. If
this is not given then shape will be NULL.

PyBUF_C_CONTIGUOUSPyBUF_F_CONTIGUOUSPyBUF_ANY_CONTIGUOUS

These flags indicate that the contiguity returned
buffer must be respectively, C-contiguous (last
dimension varies the fastest), Fortran contiguous
(first dimension varies the fastest) or either
one. All of these flags imply
PyBUF_STRIDES and guarantee that the
strides buffer info structure will be filled in
correctly.

PyBUF_INDIRECT

This flag indicates the returned buffer must have
suboffsets information (which can be NULL if no
suboffsets are needed). This can be used when
the consumer can handle indirect array
referencing implied by these suboffsets. This
implies PyBUF_STRIDES.

PyBUF_FORMAT

The returned buffer must have true format
information if this flag is provided. This would
be used when the consumer is going to be checking
for what ‘kind’ of data is actually stored. An
exporter should always be able to provide this
information if requested. If format is not
explicitly requested then the format must be
returned as NULL (which means 'B', or
unsigned bytes)

Fill in a buffer-info structure, view, correctly for an exporter that can
only share a contiguous chunk of memory of “unsigned bytes” of the given
length. Return 0 on success and -1 (with raising an error) on error.

Create a memoryview object wrapping the given buffer-info structure view.
The memoryview object then owns the buffer, which means you shouldn’t
try to release it yourself: it will be released on deallocation of the
memoryview object.

Create a memoryview object to a contiguous chunk of memory (in either
‘C’ or ‘F’ortran order) from an object that defines the buffer
interface. If memory is contiguous, the memoryview object points to the
original memory. Otherwise copy is made and the memoryview points to a
new bytes object.

Return a pointer to the buffer-info structure wrapped by the given
object. The object must be a memoryview instance; this macro doesn’t
check its type, you must do it yourself or you will risk crashes.

A “buffer object” is defined in the bufferobject.h header (included by
Python.h). These objects look very similar to string objects at the
Python programming level: they support slicing, indexing, concatenation, and
some other standard string operations. However, their data can come from one
of two sources: from a block of memory, or from another object which exports
the buffer interface.

Buffer objects are useful as a way to expose the data from another object’s
buffer interface to the Python programmer. They can also be used as a
zero-copy slicing mechanism. Using their ability to reference a block of
memory, it is possible to expose any data to the Python programmer quite
easily. The memory could be a large, constant array in a C extension, it could
be a raw block of memory for manipulation before passing to an operating
system library, or it could be used to pass around structured data in its
native, in-memory format.

Return a new read-only buffer object. This raises TypeError if
base doesn’t support the read-only buffer protocol or doesn’t provide
exactly one buffer segment, or it raises ValueError if offset is
less than zero. The buffer will hold a reference to the base object, and
the buffer’s contents will refer to the base object’s buffer interface,
starting as position offset and extending for size bytes. If size is
Py_END_OF_BUFFER, then the new buffer’s contents extend to the
length of the base object’s exported buffer data.

Changed in version 2.5: This function used an int type for offset and size. This
might require changes in your code for properly supporting 64-bit
systems.

Return a new writable buffer object. Parameters and exceptions are similar
to those for PyBuffer_FromObject(). If the base object does not
export the writeable buffer protocol, then TypeError is raised.

Changed in version 2.5: This function used an int type for offset and size. This
might require changes in your code for properly supporting 64-bit
systems.

Return a new read-only buffer object that reads from a specified location
in memory, with a specified size. The caller is responsible for ensuring
that the memory buffer, passed in as ptr, is not deallocated while the
returned buffer object exists. Raises ValueError if size is less
than zero. Note that Py_END_OF_BUFFER may not be passed for the
size parameter; ValueError will be raised in that case.

Changed in version 2.5: This function used an int type for size. This might require
changes in your code for properly supporting 64-bit systems.

Return a new writable buffer object that maintains its own memory buffer of
size bytes. ValueError is returned if size is not zero or
positive. Note that the memory buffer (as returned by
PyObject_AsWriteBuffer()) is not specifically aligned.

Changed in version 2.5: This function used an int type for size. This might require
changes in your code for properly supporting 64-bit systems.